Femoroacetabular impingement has emerged as a cause of osteoarthritis of the young hip. This article presents a modified open procedure for cases that cannot be completely managed arthroscopically.
Femoroacetabular impingement is considered responsible for many young, nondysplastic, osteoarthritic hips. According to that theory, repetitive conflict between the head–neck junction and acetabular rim can determine degenerative modifications in the labrum and chondral surfaces up to advanced osteoarthritis.
The hip joint clearance is wide enough to avoid conflict if femoral and acetabulum anatomy is normal. Congenital or acquired changes in head–neck offset and acetabular coverage may reduce clearance and induce femoroacetabular impingement.
Impingement has been detected mainly in the anterolateral part of the joint; thus, liable movements are flexion and internal rotation. Clinical observations confirm this hypothesis because patients often refer symptoms to this position.
Pain in flexion-internal rotation of the hip is known as impingment sign.3 Although extremely sensitive, the impingement sign is unspecific,because the anterolateral labrum frequently is involved by early osteoarthritis and primary labral lesions. Thus, the physical examination always should be followed by adequate imaging: a standing anteroposterior view of the pelvis, a lateral view, and a false profile view to detect gross femoral and acetabular abnormalities.
Dynamic fluoroscopic examination represents the gold standard in demonstrating the conflict, but the significant exposure of both the operator and the patient prohibits routine use.
A computed tomography (CT) scan or magnetic resonance imaging (MRI) should be obtained before any surgical decision, as they allow more precise evaluations of cartilage thickness, labral lesions and ossification, and exact acetabular version. We prefer CT scans in acetabular anomalous coverage, as it outlines the bony margins of the socket. Although arthro-MRI and arthro-CT scans seem to be more sensitive in detecting labral detachments, we do not consider them essential.

With regard to the pathophysiology, two mechanisms have been postulated to explain degenerative arthropathy originated by femoroacetabular impingement: cam effect and pincer effect.
Cam effect is determined by aspherical heads in which radius increases from the central zone to the peripheral one. The anomalous head shows a “pistol grip shape” in the anteroposterior view because it is abnormally extended over the anterolateral part of the neck (Figure 1). When the abnormal part of the head is forced into the socket by flexion-internal rotation, it generates shear forces against the cartilage of the anterosuperior quadrant of the acetabulum. This stress produces abrasion and then chondropathy. The labrum is just partially involved.4
Pincer effect is the linear contact between a normal neck and an overcovering rim. This occurs in hips affected by acetabular retroversion and by coxa profunda. In the former type of dysplasia the overcoverage is selective for the anterosuperior quadrant of the socket; in the latter type, it is general (Figures 2-4). According to Ruelle and Dubois,5 coxa profunda is a mildly deepened acetabulum in which the medial wall touches the ilioischial line (or is slightly medial), and protrusio is extremely deepened with the femoral head overlapping the ilioischial line.
Pincer femoroacetabular impingement is characterized by labral lesions up to its complete ossification. Chondral lesions may be present in the opposite posteroinferior quadrant because of the repetitive leverage of the head on the anterosuperior rim. In fact, while the head is partially levered out of the socket, dislocation is resisted by the shear stress between the head and the opposite side of the acetabulum. Less important cartilage involvement makes pincer femoroacetabular impingement more benign than cam femoroacetabular impingement.